1. Technical Field
The present invention relates to an image forming apparatus, and particularly, to an image forming apparatus adapted to make a print on an envelope.
2. Background Arts
There are remarkably widespread inkjet printers spread as image forming apparatuses capable of high-speed color printing, costing low. Most types of inkjet printers are connectable to a terminal, such as a personal computer, to take in image data, such as letters, illustrations, and marks, produced at the terminal, to print the images on sheets. Some composite types of inkjet printers have an integrated scanner for taking in image data as data through the scanner, to print them. Some composite types of inkjet printers have an integrated facsimile for receiving image data as data transferred to the facsimile, to print them.
Inkjet printers form images by printing on a recording medium such as a sheet of plain paper, photo paper, inkjet-oriented paper, mat paper, or an OHP film. Inlet printers employed for domestic services make a print on a selective one of recording mediums between the size of postcards and the size of A4 paper. Inkjet printers employed for office services make a print on a selective one of recording mediums between for instance the postcard size and the size of A3 paper.
Inkjet printers have enhanced performances such as print speed and print quality. Enhancements in such performances are accompanied by spread demands for using inkjet printers to print lots of envelopes for advertisement. Typically inkjet printers make a print on a single planer sheet of recording medium. It is therefore possible to adjust with ease a head gap between an array of print heads and a recording medium to be transferred in a printing section of an inkjet printer. The adjustable head gap affords to avoid interferences between the print head array and the recording medium. This allows for a printing free from troubles such as failures in transfer of recording medium (e.g. jamming), deformation of recording medium (e.g. turn-up), or degradation of print quality (e.g. stain).
However, since envelopes have a profile varied in part, it is difficult to have a head gap secured over the length or width of an envelope. As a result, variations in head gap tend to cause interferences between an envelope and print heads. This makes the printing of envelope difficult. Typical envelopes are each designed to enclose a flat object such as a letter or card, and produced as an enclosure from a four-sided sheet, by folding three of four triangular corners of the sheet around a central rectangular area. This enclosure includes a rectangle-faced body (referred herein to as an envelope body) that has the above three corners folded at three sides thereof and sealed to close on the reverse. The enclosure has one of the above four corners (referred herein to as a flap) to be folded to close at the remaining one side of the envelope body after an object such as a letter or card is enclosed. Accordingly, the envelope body includes those regions in which two sheet areas overlap each other, and those regions in which two or more glued sheet areas overlap another sheet area. As a result, the envelope body has a thickened profile varied in part even before enclosing an object. On the other hand, the flap extends as a single sheet area in the open state before being folded, in which the profile is thin. However, when the flap is folded back to close, it overlaps one or more sheet areas. In this state, the envelope has a profile thickened over those regions of the envelope body covered by the flap. The envelope may have an internal enclosure accommodated therein. In such a case, there may be an increased number of sheet areas overlapping each other. Inkjet printers may be used to print a destination's address, company name, personal name, and the like on a front side of an envelope, and a sender's address, company name, personal name, and the like on a backside of the envelope.
There has been disclosed in the Japanese Patent Application Laid-Open Publication No. 5-94067 an electro-photographic device for printing data such as an address and the like on a backside of an envelope having a flap in a closed state. This electro-photographic device has been devised to avoid hiding a part of the data printed on a backside of an envelope when a flap of the envelope is closed after the printing on the backside of the envelope having the flap left as it was open.